Few details have emerged so far about the how the September attack was masterminded or how gunmen held off Kenyan security forces for four days in the Westgate mall. The assault was claimed by the Somali Islamist group al Shabaab.

U.S., British, Israeli and other experts joined Kenyan investigators at the site of the attack, which struck at the heart of east Africa's biggest economy. The West sees Kenya as vital to the regional fight against militant Islam.

All the men who appeared in court on Monday were formally charged with "commission of a terrorist act" under Kenya's anti-terrorism laws. Other accusations ranged from providing support and shelter to the gunmen to using false documents.

The suspects all pleaded not guilty at the hearing. The men were named as Mohamed Ahmed Abdi, Liban Abdullah Omar and Hussein Hassan, while a fourth was identified as Adan Mohamed Ibrahim, although he was listed as using other aliases.

Last month, Kenya named four gunmen who took part in the assault. Al Shabaab said it acted because of Kenya's refusal to withdraw its troops from Somalia where they are part of a African peacekeeping force battling the militants.

The court is expected to set a formal date for the start of trial on November 11. The men were remanded in custody until then.